1. Field of the Invention
This invention relates generally to shaft seals. More specifically, this invention relates to a seal for a housing having an opening through which a shaft passes and the shaft undergoes rotary and axial motion.
2. Description of the Prior Art
Gears trains, pumps and other mechanical drive assemblies are usually located in a housing having a lubricating environment which is ideally is free of atmospheric contaminants such as dirt, moisture, and corrosive chemicals. Shafts for delivering power to such assemblies typically pass through an opening in the housing. In order to keep contaminants out and lubricants in, seals are provided at the opening between the housing and the shaft. Any leakage around this seal can result in a loss of lubricating fluid or entry of contaminants into the housing environment with either condition leading to reduced output or mechanical failure of the drive assembly.
A shaft transmitting power into a housing may undergo rotary motion, axial motion, or both. Acceptable seals for preventing leakage around the shaft and housing for either axial or rotary motion are well-known. However, such seals are specifically suited for only one type of shaft motion. For instance, when there is rotary motion of a shaft relative to the housing, the housing may be sealed with a seal having a relatively thin and flexible lip portion; this allows the seal to compensate for shaft run-out, i.e. eccentric rotation of the shaft, without generating excessive heat. Allowing this flexibility for shaft run-out gives the gasket poor lateral stiffness thereby making the gasket susceptible to buckling in the event of axial rod movement. Furthermore, the reduced cross section makes it easier for fluid or particulates on the shaft to slide past the seal when the shaft moves axially with respect to the seal surface. Conversely, a seal designed for axial movement of a shaft with respect to a housing or seal has a relatively large cross section and a stiff lip portion that is designed to scrape particulates or lubricants from the shaft as it moves across the face of the seal. The greater stiffness of the axial seal compared to the rotary seal is necessary to withstand the buckling forces that axial movement of the shaft generates. The increased radial stiffness of the axial seal is also necessary to maintain contact around the entire circumference of the shaft so that the desired scraping effect is achieved. However, this increased stiffness restricts movement of the seal under shaft run-out so that increased friction between the axial seal and the shaft generates high heat and can cause premature failure of the gasket under rotational conditions. Therefore, no single seal element is presently available that can provide adequate and sustained sealing around a housing opening for a shaft that is undergoing axial and rotary motion.
A good example of an instance where a shaft passing into a housing undergoes axial and rotary motion is in the case of a pivotable drive axle assembly. A typical example of such an arrangement is the steerable drive axle of a vehicle as shown in U.S. Pat. No. 3,605,930 issued to Ainsworth. In the Ainsworth patent, a drive shaft transfers power to a driven shaft in a knuckle housing which is pivotally attached to a yoke housing the drive shaft. The Ainsworth patent uses a Cardan-type joint to transfer power from the drive shaft to a sun shaft housed in the knuckle. As the knuckle assembly is pivoted relative to the yoke, angularity is introduced into the universal joint. In an angled condition, rotation of the shafts causes variation in axial length across the universal joint. Thus as the drive shaft transfers rotary power to the sun shaft across the angled universal joint, of either or both shafts reciprocating motion results. These shafts pass through the knuckle and yoke into lubricating environments separated from the atmosphere by seals at the knuckle and yoke openings. Accordingly, it is necessary to have a seal at at least one opening that can withstand relative axial and rotary movement of a shaft passing therethrough.
One approach to the problem in the case of steerable drive axles has been to use an axially restrained type universal joint which eliminates the reciprocating motion of the shafts when the universal joint is turned at an angle. An example of this type of universal joint is shown in U.S. Pat. No. 2,046,584 issued to Rzeppa. A steerable drive axle using an axially restrained universal joint is shown in U.S. Pat. No. 4,482,025. However, these universal joints are more expensive than Cardan-type joints and require a large boot to seal internal elements of the joint. Aside from the added cost, the possibility of boot rupture when a vehicle operates in rough terrain adds an additional failure mode to the steerable drive axle. Therefore, it is desirable to have a seal that will allow the use of a Cardan-type joint in a steerable drive assembly.
Accordingly, it is an object of this invention to provide a seal for an opening through which a shaft passes which can withstand rotary and axial movement of the shaft.
It is a further object of this invention to improve the reliability of seals around a shaft opening when the shaft has axial and rotary motion.
It is a further object of this invention to provide a seal for a drive shaft in a pivotable drive axle assembly using a Cardan-type universal joint.